The present invention relates to a suction roll, which is particularly useful for a single-wire dryer group of a paper making machine. In such a dryer group, a web, for instance, a paper web, which is to be dried travels, together with a porous support belt, alternately over dryer cylinders and suction rolls. The suction rolls serve primarily as reversing rolls for the support belt and for the web which is carried along by the support belt. The web of paper is pressed against the dryer cylinders by the support belt. As the support belt travels over the reversing rolls, however, the support belt is between the outside of the reversing rolls and the paper web. At the reversing rolls, the web must be drawn by suction against the support belt and in opposition to the centrifugal force which acts on the web. For this reason, the reversing rolls are developed as suction rolls.
The invention relates to a suction roll which does not include the usual suction box. In known box suction rolls, a stationary suction box extends through the hollow roll body. A suction box-less suction roll, of which the invention is an example, is known from EP-A 0332599 which is equivalent to U.S. Pat. No. 5,022,163. With this type of suction roll, it has been found that the consumption of energy for producing a given vacuum on the outside of the shell of the roll increases with the operating speed of the machine that is, increases with the speed of rotation of the suction rolls.